One type of ink-jet printer employs ink that is solid under ambient conditions and is heated to a liquid state during the printing operation. The solid ink is stored in a reservoir that has a print head mounted to it. The print head includes a plurality of chambers into which the liquified ink flows. Each chamber has a contiguous orifice. The mechanism for ejecting the liquified ink from a chamber through a particular orifice may employ, for example, a minute heater, such as a thin-film resistor, that is instantaneously heated by a pulse of current directed through the resistor. The instantaneous heating of the resistor vaporizes a portion of the ink that is adjacent to the resistor, and the attendant expansion of the fluid in the chamber ejects a droplet of ink from the orifice to the paper or other print media that is advanced through the printer adjacent to the print head.
Such an ink-jet printer is permitted to cool when the printer is not being operated, so that the ink solidifies. As the ink solidifies, its volume decreases, as it melts its volume increases. This melting and heating cycle, along with operation of the droplet ejection mechanism just mentioned, leads to entrapment of gas bubbles within the ink. Gas bubbles are undesirable because they cause variations in the size and trajectory of the ink droplets, or may lead to complete depriming and failure of an ink-jet print head at one or more orifices.
This invention is directed to an apparatus and method for controlling the heating and cooling of solid ink in ink-jet printing in a manner such that gasses that may be trapped in the ink are directed away from the ink-jet print head to a location where they may be collected and purged from the ink supply system.
As one aspect of the invention, the heating of the ink is controlled so that the ink-jet print head may be reprimed prior to each operation of the printer.
As another aspect of the invention, heaters are provided for melting the solid ink. The heaters are configured and arranged to facilitate the removal of gasses trapped within the ink once the heaters are turned off.